The cutting rollers of road milling machines, mining machines or the like are usually provided with chisel holder changing systems. In this instance, base portions of the chisel holder changing systems can be connected to the surface of a cutting roller pipe, in particular welded or screwed thereto. In this instance, the base portions are positioned relative to each other so that helical loading members are produced on the surface of the cutting roller. Chisel holders are connected to the base portions, wherein the chisel holders may be screwed, welded or otherwise retained with respect to the base portion, for example, clamped. In the simplest case, the chisel holders may also be directly connected to the surface of a cutting roller pipe. The chisel holders have a chisel receiving member. The chisels described above can be mounted therein so as to be able to be replaced. During use of the machine, the chisels strike with the chisel tips thereof the substrate which is intended to be removed and cut into it. In this instance, the ground material is broken up. The material which has been removed in this manner can be transported, for example, via the helical broaching and loading members toward the center of the cutting roller and conveyed out of the operating region of the cutting roller at that location by means of ejectors. The material can then be transported away using appropriate devices, for example, transport belts. The chisels are provided with chisel tips, which comprise hard material and which bring about the cutting engagement. They are consequently subjected to an abrasive attack and must therefore comprise a suitable hard material in order to achieve the longest possible service-life. From the prior art there are known chisels in which the chisel tip comprises hard metal. In order to be able to generate uniform wear at the periphery with such chisels, the chisels are generally rotatably arranged in chisel receiving members of the chisel holders.
There are also known chisels which are provided in the region of the chisel tips thereof with a “superhard material”. For example, the chisel tips have a coating of polycrystalline diamond or another material which has a hardness which is comparable with diamond. Such a chisel is known from US 2012/0080930 A1. Such chisel tips have an extraordinarily long service-life and exhibit hardly any wear during operational use. It is therefore not absolutely necessary to fix these chisels in a rotatable manner in the chisel holders. US 2012/0080930 A1 therefore proposes providing the chisel shaft of the chisel with a thread and clamping the chisel securely to the chisel holder by means of a nut. If after a specific operating time wear appears on the chisel, the nut can be released, the chisel can be rotated slightly and the nut can then be retightened.
In this instance, in the spatial distance between the outer periphery of the nut and the inner periphery of a holder receiving member in which the nut is inserted, a tool wrench is inserted. The rear region of the chisel holder which forms the holder receiving member can be accessed only with difficulty so that the chisel change is complex. In addition, ground material which is removed during operational use can be introduced in the spatial distance mentioned above and be compressed therein. The spatial distance then has to be scratched free. The clearance of the spatial distance is particularly complex in road milling machines since the bitumen material which has been removed sets hard as a sticky mass in the spatial distance. This results in long machine downtimes for the chisel change.
Another disadvantage is that no indexing is provided, that is to say, the chisel can be clamped in any position which is rotated about the longitudinal axis thereof. Once released it can hardly be clamped again any more in the same position, be clamped again in a position rotated through a specific angle or be clamped again at the same angle as an adjacent chisel.